Telechelic polyisobutylenes (PIBs) are of great commercial and scientific interest. Specifically, allyl-telechelic polyisobutylene (allyl-PIB-allyl), which can be made only by living polymerization, is the key ingredient for the preparation of biostable PIB-based polyurethanes, and various adhesives and sealants. Allyl-PIB-allyl is also an intermediate for the preparation of block copolymers, potting gels, surfactants, pressure sensitive adhesives, and non-stick chewing gum. Living IB polymerizations are most valuable for the preparation of predictable molecular weights and narrow dispersity products. The significance of this methodology, however, goes far beyond molecular weight (MW) and molecular weight distribution (MWD) control, and, in addition to making allyl-PIB-allyl, it can be used for the preparation of a great variety of telechelics, block polymers, etc.
The synthesis of allyl-PIB-allyl at cryogenic temperatures has been described. See, B. Ivan, J. P. Kennedy, J. Polym. Sci., Part A: Polym Chem. 1989, 28, 89-104 and J. P. Kennedy, B. Ivan, In Designed Polymers by Carbocationic Macromolecular Engineering; Hanser Verlag, Munich, 1992, the disclosures of which are incorporated herein by reference. Traditionally, the cooling of isobutylene (IB) polymerization charges to low temperatures is necessary to “freeze out” undesirable side reactions during polymerization, the most deleterious of which is chain transfer to monomer. This side reaction produces two polymer molecules with unsaturated end groups, i.e., an exo and an endo unsaturation, by proton loss of the propagating tertiary cation, plus a new tert butyl cation that sustains further propagation (See, Scheme 1, below).

The predominant product of chain transfer is the polymer carrying the exo double bond while that with endo unsaturation is a minor component. Mechanistic details of chain transfer are beyond the scope of this application and have been described elsewhere. See generally, G. Erdodi, J. Kang, J. P Kennedy, E. Yilgor, I. Yilgor, J. Polym. Sci.: Part A: Polym. Chem., 2009, 47, 5278-5290 and Published U.S. Patent Application No. 1988/4758631 to Kennedy et al., the disclosures of which are incorporated herein by reference.
Another undesirable side reaction that can occur in these reactions involves the active propagating cation plus the exo double bond at the terminus of a polymer formed by deprotonation (see, Scheme 1, above). This alkylation followed by proton loss (sometimes called “coupling”), yields ill-defined high molecular weight byproducts (See, Scheme 2, below).
It is known that these undesirable reactions may occur if the polymerization is carried out at a relatively high temperature or is not quenched (terminated) as soon as practicable after complete monomer conversion and the system remains active in the absence of monomer.
The rate of IB polymerization in these living cationic polymerization reactions is very high, virtually instantaneous upon coinitiator addition, and monomer conversions reach near completion within seconds. Thus, it has been very difficult to obtain rate constants needed for designing process conditions. Further, the polymerization is known to be highly exothermic, making it is very difficult to maintain a constant reaction temperature. And if the heat of reaction is not completely removed and the temperature increases, byproduct formation by side reactions increases. In practice, the high heat of reaction is mitigated by the use of costly high efficiency stirrers and special cooling equipment.
It has been known for some time that refluxing solvents may be used to mitigate heat evolution of exothermic reactions. Under reflux conditions the heat of polymerization is instantaneously absorbed by the refluxing medium and the temperature remains unchanged. The heat generated during exothermic polymerization merely increases the rate of reflux and the temperature does not change because it is set by the boiling point of the system. The increased rate of reflux is also beneficial as it contributes to the mixing of the charge and obviates the use of high cost stirring and cooling equipment. On reaction completion, the refluxing solvent(s) can be easily removed by evaporation at room temperature, recovered and reused. Thus, product recovery is facilitated and cumbersome workup is avoided or simplified.
What is needed in the art is a method for the synthesis of allyl-PIB-allyl with quantitative allylation of living ends using living cationic polymerization under ideal temperature control, or at least increased temperatures, using refluxing solvents.